Where did you get those calculations from?
So, "If miners decide to sell all their mined Bitcoins, (or 50%)" wasn't enough of a clue for you?
It is built in the Bitcoin design that in a steady state almost all of the mining rewards are spent on the electricity costs. Until the point where you can pay your electricity costs in BTC, this money must pass trough the exchanges, which pushes the price down.
In other words, Bitcoin has built-in price brakes. The higher the Bitcoin price is, the higher the downwards pressure becomes.